Field of the Invention
The invention the subject of the present application relates to the expansion of particulate tobacco.
In United Kingdom Patent Specification No. 2 176 385A there is disclosed tobacco expansion apparatus comprising a transport duct, gaseous supply means operable to supply hot gaseous medium to the duct at an upstream end thereof, feed means operable to feed particulate tobacco to the duct, and a tobacco/gaseous medium separator, the gaseous medium inlet of which separator is in gas flow communication with the downstream end of the duct. The tobacco/gaseous medium separator is of a type in the operation of which the tobacco particle residence time therein is exceptionally low. For this reason the overall residence time of tobacco particles in the expansion aparatus is low. The overall residence time may be, for example, less than two seconds, or even less than one second. It should be possible, because of the low overall tobacco particle residence time obtainable in the operation of the expansion apparatus of UK No. 2 176 385A to employ a high temperature gaseous medium without the tobacco particles being subjected to an over intensive heating regime. The temperature of the gaseous medium at entry to the transport duct may be, for example, at or above 250.degree. C., more usually at or above 350.degree. C.
A problem that can occur in the use of tobacco expansion apparatus such as that just mentioned is that, should the mass flow rate of the tobacco fall below the specified value therefore, there will be a tendency for tobacco particles to be unacceptably over heated. If, on the other hand, the mass flow rate of the tobacco is greater than that specified, insufficient heat will transfer to the tobacco particles for the particles to be expanded according to specification. The first of these problems is a function of the high heat content of the gaseous medium and the second arises from the short residence time characteristic of the apparatus.
It is an object of the subject invention to obviate the just mentioned problems in the expansion of tobacco in apparatus operable to bring the tobacco into contact, over a short contact time, with hot gaseous medium.